The present invention relates to a screen printing apparatus for printing paste such as cream solder or conductive paste on a substrate.
In an electronic part mounting process, the screen printing process is employed as the method of printing paste such as cream solder or conductive paste on a substrate. This screen printing method is performed in a manner that a mask plate in which pattern holes are perforated in accordance with portions to be printed is set on a substrate and paste is printed on the substrate through the pattern holes of the mask plate by the squeegeeing process.
As the squeegeeing method for the screen printing, there is known the method of using the enclosed-type squeegee head. According to this method, unlike the usual screen printing method, paste is not directly supplied on a mask plate but a squeegee head reserving paste therein is employed. Conventionally, the enclosed-type squeegeeing head is employed in a manner that the paste within the squeegee head is pressurized by a pressurizing means such as a piston thereby to perform the filling operation of the paste within pattern holes mainly by the pressure.
However, according to the screen printing method using the conventional enclosed-type squeegeeing head, since the paste is always placed in a pressurized state in the squeegeeing process, a problem due to leakage of the paste likely occurs. For example, at the abutment portion between the upper surface of the mask plate and a blade provided at the lower surface of the squeegee head, the paste is prevented from bulging out by pressing the blade against the mask plate with a suitable surface pressure. However, the surface pressure value is not always constant and both the pressurizing state and the viscosity of the paste vary with time, so that it is difficult to prevent the leakage of the paste stably.
Further, the heights of the printing surface vary due to the presence of a resist layer depending on a substrate to be printed. Thus, when the mask plate is attached to such a substrate, a gap appears likely between the mask plate and the substrate. When the enclosed-type squeegee head is employed for the mask plate in such a state, there arises a problem that the pressurized paste bulges out and moves into the gap through the pattern holes. In this manner, the conventional enclosed-type squeegee head has the problem that the paste leaks or bulges out due to the pressurizing of the paste within the squeegee head.
Accordingly, an object of the invention is to provide a screen printing apparatus which can eliminate a problem caused by the leakage of paste and realize preferable printing.
The screen printing apparatus according to the invention is arranged in a manner that in the screen printing apparatus in which a squeegee head is moved on a mask plate thereby to print paste on a substrate through pattern holes of the mask plate, the screen printing apparatus comprises: horizontally moving means and elevation means for moving in a horizontal direction and elevating the squeegee head with respect to the mask plate; pressing means for pressing the squeegee head against the mask plate; a printing space which is provided at the squeegee head and reserves the paste therein and makes the paste contact with a surface of the mask plate through an opening portion formed at a lower surface of the printing space; a partition portion which forms front and rear walls in a squeegeeing direction of the printing space and partitions between the printing space and outside; and a filling portion which forms front and rear edges of the opening portion and fills the paste within the pattern holes in a squeegeeing process.
According to the invention, the screen printing apparatus is arranged to include the printing space which is provided at the squeegee head and reserves the paste therein and makes the paste contact with the surface of the mask plate through the opening portion formed at the lower surface of the printing space; the partition portion which forms the front and rear walls in the squeegeeing direction of the printing space and partitions between the printing space and the outside; and the filling portion which forms the front and rear edges of the opening portion and fills the paste within the pattern holes in the squeegeeing process. Thus, the paste can be filled into the pattern holes without pressurizing the paste, and the problem caused by the leakage of the paste can be eliminated and preferable printing can be realized.